Field
The invention relates generally to medical devices and procedures pertaining to prosthetic heart valves. More specifically, the invention relates to replacement of heart valves that have malformations and/or dysfunctions. Embodiments of the invention relate to prosthetic heart valves for replacing a mitral valve in the heart, or for replacing other valves where an additional ring or other anchor is utilized together with the prosthetic heart valve at the implant site, and assembly methods for preparing such prosthetic heart valves for implantation.
Description of Related Art
Referring first generally to FIGS. 1 and 2, the mitral valve controls the flow of blood between the left atrium and the left ventricle of the human heart. After the left atrium receives oxygenated blood from the lungs via the pulmonary veins, the mitral valve permits the flow of the oxygenated blood from the left atrium into the left ventricle. When the left ventricle contracts, the oxygenated blood held in the left ventricle is delivered through the aortic valve and the aorta to the rest of the body. Meanwhile, the mitral valve closes during ventricular contraction, to prevent the flow of blood back into the left atrium.
When the left ventricle contracts, the blood pressure in the left ventricle increases substantially, and urges the mitral valve closed. Due to the large pressure differential between the left ventricle and the left atrium during ventricular contraction, a possibility of prolapse, or eversion of the leaflets of the mitral valve back into the atrium, arises. To prevent this, a series of chordae tendineae connect the mitral valve to the papillary muscles along opposing walls of the left ventricle. The chordae tendineae are schematically illustrated in both the heart cross-section of FIG. 1 and the top view of the mitral valve in FIG. 2. Just before and during ventricular contraction, the papillary muscles also contract and maintain tension in the chordae tendineae, to hold the leaflets of the mitral valve in the closed position and preventing them from turning inside-out and back into the atrium, thereby also preventing backflow of the oxygenated blood into the left atrium.
Complications of the mitral valve can potentially cause fatal heart failure. One form of valvular heart disease is mitral valve leak, also known as mitral regurgitation, characterized by the abnormal leaking of blood from the left ventricle back into the left atrium through the mitral valve. In these circumstances, it may be desirable to repair the mitral valve or to replace the functionality of the mitral valve with that of a prosthetic heart valve.
Up to this point, mitral valve repair has been more popular than valve replacement, since there were previously little or no effective commercially available ways to replace a mitral valve through catheter implantation and/or other minimal or less invasive procedures.
Replacement of a mitral valve is difficult in many respects, for example, due to the physical structure of the valve and difficulties in accessing the valve. The most prominent obstacle for mitral valve replacement is anchoring or retaining the valve in position, due to the valve being subject to a large cyclic load. Especially during ventricular contraction, the movement of the heart and the load on the valve can combine to shift or dislodge a prosthetic valve. Also, the movement and rhythmic load can fatigue materials, leading to fractures of the implanted valve. If the orientation of a mitral prosthesis is unintentionally shifted, blood flow between the left atrium and the left ventricle can be obstructed or otherwise negatively affected. While puncturing the tissue in or around the mitral valve annulus to better anchor an implanted valve is an option for retaining the placement of the implant, this can potentially lead to unintended perforation of the heart and patient injury.
Another issue with mitral valve replacement is the size and shape of the native mitral valve. A general shape of the mitral valve and its leaflets as seen from the left atrium is illustrated in FIG. 2. The mitral valve annulus is quite large and non-circular, when compared for example, to the more circular aortic valve annulus, where valve replacement is more prominent. As such, a circular prosthetic mitral valve that is too small can cause leaks around the implanted valve (i.e., paravalvular leak) if a good seal is not established around the valve. Meanwhile, a circular valve implant that is too large can stretch out and damage the native valve annulus.